The present invention relates to implantable neurostimulator systems, such as cochlear implants, and more particularly to an algorithm for use in a cochlear implant for optimizing pitch (frequency) and other speech stimuli allocation.
At present, very few cochlear implant patients are able to enjoy music. This is due, in part, to the fact that in the generation of control programs that allocate the stimuli to selected electrodes, or groups of electrodes, of the electrode array adapted to be inserted into the cochlea, no compensation is made for pitch warping.
Attempts have been made in the past to better allocate pitch based on recognizable speech stimuli, such as vowel sounds. See, Harnsberger, et al., “Perception “vowel spaces” of cochlear implant users: Implications for the study of auditory adaptation to sepctral shift,” J. Acoust. Soc. Am., Vol. 109, No. 5, Pt. 1, pp. 2135-45 (May 2001). Such attempts to use vowel sounds have not resulted in great success.
Within the cochlea, there are two main cues that convey “pitch” (frequency) information to the patient. They are (1) the place or location of stimulation; and (2) the temporal structure of the stimulating waveform. In existing cochlear implant devices, frequency is mapped to a “place” as defined by the position of the electrode. Along the electrode array, frequencies are progressively mapped from low to high in the apical to basal direction, respectively. Unfortunately, the position of the electrode is not very precise, i.e., there are only a limited number of electrodes, e.g., 16 to 24, spread along the length of the electrode which is inserted into one of the spiraling ducts of the cochlea. Hence, mapping to a “place” within the cochlea has heretofore not been a very precise operation. Further, in existing cochlea implants, very little attention has been given to the waveform of the stimulating current, with only one or two parameters (e.g, amplitude and pulse width) being adjustable. Hence, it is seen that in existing cochlea implants, of the two main cues that convey pitch information, one (“place”) has been addressed only imprecisely, and the other (“waveform”) has only been addressed in a limited manner.
It is thus seen that improvements are needed in the way that a cochlear implant conveys pitch information to a user.